Speaker
The poem's speaker is a heartbroken person about to part from a lover, seemingly forever. He comes across as romantic, devoted, and extremely sad. His descriptions of his feelings for the lover are hyperbolic and adoring, but his descriptions of his own heartbreak are perhaps even more vivid, making use of vivid sensory images and figurative language. The poem's regimented structure and repetitiveness reveal that the speaker feels trapped, out of control, and exhausted.
Nancy
The opening lines of the second stanza reveal that the lover being addressed is named Nancy. It is likely that "Nancy" refers to Agnes MacLehose, a married woman with whom the poet had a relationship, but the actual lover described in the poem is elusive and vaguely described as if the speaker is already losing sight of her. He describes her as beautiful and impossible not to love, but avoids specific images or anecdotes, making her something of a mystery. One thing does seem clear about Nancy, though: she is likely just as sad to part with the speaker as he is to part with her. His use of the first-person plural in statements like "We had ne'er been broken-hearted" hints that she, too, is brokenhearted.
